1. Field of the Invention
The invention relates to a scribing apparatus for a liquid crystal display that occupies little space and enhances productivity, a substrate cutting apparatus equipped with the scribing apparatus, and a substrate cutting method using the substrate cutting apparatus.
2. Discussion of the Related Art
LCD devices display a desired image by individually supplying image data signals according to liquid crystal cells arranged in a matrix array, thereby controlling respective light transmittances of the liquid crystal cells.
The manufacture of such LCD devices utilizes a large-area mother substrate on which thin film transistor (TFT) array substrates are formed. Another large-area mother substrate, on which color filter (C/F) substrates are formed, is used. In order to achieve an improvement in throughput, the mother substrates are joined together to simultaneously form multiple of liquid crystal panels. Then, it is necessary to perform a process to cut the joined mother substrates into unit liquid crystal panels.
The liquid crystal panel cutting process generally includes a scribing process to form a crack to a desired depth in a surface of a mother substrate by using a scribing wheel made of a diamond material having a hardness higher than that of the mother substrate, which is made of, for example, glass. A breaking process applies a mechanical force to the mother substrate, thereby cutting the mother substrate.
FIG. 1 shows a sectional view illustrating a related art LCD device. This LCD device is manufactured in accordance with the following method. For simplicity, the following description will be given only in conjunction with one pixel region.
FIG. 1 shows a gate electrode 11 made of a conductive material such as metal that is initially formed on a first transparent substrate 10 at a predetermined region. A gate insulating film 12 made of a silicon nitride (SiNx) or silicon oxide (SiO2) is then formed over the entire upper surface of the first substrate 10 including the gate electrode 11.
Thereafter, an active layer 13 made of amorphous silicon is formed on the gate insulating film 12 at a region corresponding to the gate electrode 11. An ohmic contact layer 14 is formed on the active layer 13 at regions corresponding to respective lateral edge portions of the active layer 13. The ohmic contact layer 14 is formed from doped amorphous silicon.
Source and drain electrodes 15 and 16 are made of a conductive material such as metal and are subsequently formed on the ohmic contact layer 14. The gate electrode 11 together with the source and drain electrodes 15 and 16 constitute a thin film transistor T.
Although not shown, the gate electrode 11 connects to a gate line, and the source electrode 15 connects to a data line. The gate line and data line cross each other and define a pixel region.
A protective film 17 is then formed over the entire upper surface of the first substrate 10 including the source and drain electrodes 15 and 16. The protective film 17 is made from silicon nitride, silicon oxide, or an organic insulating material. The protective film 17 has a contact hole 18 that exposes a predetermined portion of the surface of the drain electrode 16.
Thereafter, a pixel electrode 19 made of a transparent conductive material is formed on the protective film 17 at the pixel region. The pixel electrode 19 connects to the drain electrode 16 via the contact hole 18.
A first orientation film 20 is then formed over the entire upper surface of the first substrate 10 including the pixel electrode 19. The first orientation film 20 is made of, for example, polyimide, and has a surface on which the molecules of the first orientation film 20 orient in a predetermined direction.
A second transparent substrate 31 is arranged over the first substrate 10 while being vertically spaced apart from the first substrate 10 by a predetermined distance.
A black matrix 32 is formed on a lower surface of the second substrate 31 at a region corresponding to the thin film transistor T of the first substrate 10. Although not shown, the black matrix 32 also covers a region other than the pixel electrode 19.
A color filter 33 is then formed on the second substrate 31 beneath the black matrix 32. Color filters are usually arranged in the form of repeated filter patterns of red (R), green (G), and blue (B), each of which corresponds to one pixel region.
A common electrode 34 made of a transparent conductive material is subsequently formed on the second substrate 31 beneath the color filter 33. A second orientation film 35 is then formed on the second substrate 31 beneath the common electrode 34. The second orientation film 35 is made of, for example, polyimide, and has a surface on which the molecules of the second orientation film 35 orient in a predetermined direction.
The first orientation film 20 and the second orientation film 35A seal a liquid crystal layer 40 between them.
Manufacturing the above-described LCD device uses an array substrate fabrication process involving the formation of thin film transistors and pixel electrodes on a substrate to fabricate an array substrate, a color filter substrate fabrication process involving formation of color filters and a common electrode on another substrate to fabricate a color filter substrate, a liquid crystal panel fabrication process involving arrangement of the fabricated substrates, injection and sealing of a liquid crystal material, and attachment of polarizing plates to fabricate a liquid crystal panel.
FIG. 2 shows a flow chart illustrating a related art LCD manufacturing method.
FIG. 2 shows that in this method, a thin film transistor (TFT) array substrate including TFTs, and a color filter substrate including color filters are first prepared (S1).
The TFT array substrate is fabricated by repeatedly performing processes of depositing a thin film and pattering the deposited thin film. In this case, the number of masks used for patterning of thin films in the fabrication of the TFT array substrate corresponds to the number of processes used in the fabrication of the TFT array substrate. Currently, research is underway to reduce the number of masks to thus reduce the manufacturing costs.
The color filter substrate is fabricated by sequentially forming a black matrix for preventing light from leaking through a region other than pixel regions, R, G, and B color filters, and the common electrode. The color filters may be formed using a dyeing method, a printing method, a pigment dispersion method, an electro-deposition method, or the like. Currently, the pigment dispersion method finds wide use.
Afterwards, an orientation film is formed over each substrate to determine the initial alignment direction of the liquid crystal molecules (S2).
Coating a polymer thin film, and treating the surface of the polymer thin film such that the molecules of the polymer thin film on the treated surface orient in a predetermined direction form the orientation film. Generally, polyimide-based organic materials are used for the orientation film. For the orientation method, a rubbing method is generally used.
In the rubbing method, the orientation film is rubbed in a predetermined direction using a rubbing cloth. This rubbing method is suitable for mass production because of the ease of the orientation treatment. Also, the rubbing method advantageously achieves stable orientation and easy control of the pretilt angle.
An optical orientation method has recently been developed and practically used that achieves orientation using polarized beams.
Next, a seal pattern is formed at one of the two substrates (S3). The seal pattern is arranged around the region where the image is to be displayed. The seal pattern has a port for injection of a liquid crystal material, and the seal pattern prevents the injected liquid crystal material from leaking.
The seal pattern is made by forming a thermosetting resin layer having a predetermined pattern. A screen printing method uses a screen mask. A seal dispenser method using a dispenser may be used.
The screen printing method, which has process convenience, is mainly used. However, the screen printing method also has drawbacks in that poor quality product may be produced because the screen mask may come into contact with the orientation film. Furthermore, the screen mask cannot easily cope with increasing substrate sizes. For this reason, there is a gradual substitution of a seal dispenser method for the screen printing method.
Subsequently, spacers of a predetermined size are sprayed on one of the either TFT array substrate or the color filter substrate to maintain an accurate and uniform space between the two substrates (S4).
The methods for spraying spacers include a wet spray method where spacer material is sprayed while being mixed with alcohol, and a dry spray method where spacer material is sprayed undiluted. For the dry spray method, there includes an electrostatic spray method using static electricity, and an ionic spray method using pressurized gas. Since LCDs are easily damaged by static electricity, the ionic spray method is mainly used.
Thereafter, the two substrates of the LCD, i.e., the TFT array substrate and color filter substrate, are arranged such that the seal pattern becomes interposed between the substrates. In this state, the seal pattern is cured under pressure to join the substrates (S5). In this case, the orientation films of the substrates face each other, and the pixel electrodes and color filters have a one-to-one correspondence.
Next, the joined substrates are cut into single liquid crystal panels (S6).
Multiple liquid crystal panels, each of which will become one LCD device, are generally formed on one substrate sheet and are then separated into individual panels in order enhance manufacturing efficiency and reduce manufacturing costs.
The liquid crystal panel cutting process includes a scribing process to form a crack in a surface of each substrate using a scribing wheel made of a diamond material having a hardness higher than that of the substrate. The substrate can be made of, for example, glass. Then, a breaking process positions a breaking bar at a portion of the substrate where the crack is formed and applies a predetermined pressure to the breaking bar, thereby cutting the substrate in the direction along which the crack extends.
Subsequently, a liquid crystal material is injected between the two substrates of each liquid crystal panel (S7). A vacuum injection method that utilizes a pressure difference between the interior and exterior of the liquid crystal panel is mainly used to inject the liquid crystal material. Micro air bubbles may be present in the liquid crystal material injected into the interior of the liquid crystal panel, and bubbles may thus be present in the interior of the liquid crystal panel, thereby causing the liquid crystal panel to have poor quality. In order to prevent such a problem, it is accordingly necessary to perform a de-bubbling process in which the liquid crystal is maintained under a vacuum for a prolonged time to remove bubbles by outgassing.
After the liquid crystal injection is complete, the injection port is sealed to prevent the liquid crystal from leaking out through the injection port. Coating an ultraviolet-setting resin over the injection port, and irradiating ultraviolet light at the coated resin to thereby set the coated resin achieve sealing the injection port.
Next, polarizing plates are attached to the outer surfaces of the liquid crystal panel, and driving circuits are then connected to the liquid crystal panel. Thus, an LCD device is completely manufactured (S8).
FIGS. 3A to 3F illustrate sequential steps of a related art process for cutting a mother substrate for separating the mother substrate into unit liquid crystal panels, using a related art substrate cutting apparatus, through sectional views and plan views.
The process for cutting a joined mother substrate (scribing and breaking processes) is usually carried out by using a substrate cutting apparatus. In FIGS. 3A to 3F, a mother substrate (1,000 mm×1,200 mm) is illustrated on which six 18.1″ liquid crystal panels are arranged.
In the cutting process, a joined mother substrate 52 is first loaded on a table 51 included in a loader, as shown in FIG. 3A.
The joined mother substrate 52 includes a TFT substrate 52a and a color filter (C/F) substrate 52b. 
In FIG. 3A, the upper figure shows a sectional view illustrating the mother substrate 52 loaded on the table 51, and the lower figure is a plan view illustrating the mother substrate 52 on the table 51 when viewed from the top.
FIG. 3B shows that the mother substrate 52 is then inverted so that the TFT substrate 52a of the mother substrate 52 faces upward.
Then, a wheel 53 is aligned along a selected separation line on the TFT substrate 52a. The wheel 53 is made of a diamond material having a hardness higher than that of the material of the substrate, for example, glass. The wheel 53 is then moved along the separation line while rotating to form a crack having a predetermined depth and extending in a long or short-axis direction (indicated by arrows in the drawing). This operation is repeated until cracks corresponding to all separation lines on the TFT substrate 52a are formed.
Thereafter, the mother substrate 52 is inverted such that the C/F substrate 52b of the mother substrate 52 faces upward, as shown in FIG. 3C. A breaking bar 54 is then arranged on the C/F substrate 52b. 
Subsequently, a predetermined pressure is applied by the breaking bar 54, thereby completely opening the cracks. As a result, the TFT substrate 52a cuts along the cracks, so that the TFT substrate 52a separates into unit liquid crystal panels.
Next, the wheel 53 is aligned with a selected separation line on the C/F substrate 52b, as shown in FIG. 3D.
The wheel 53 is then moved along the separation line while rotating to form a crack having a predetermined depth and extending in a long or short-axis direction (indicated by arrows in the drawing). This operation is repeated until cracks corresponding to all separation lines on the C/F substrate 52b are formed.
Thereafter, the mother substrate 52 is then inverted such that the TFT substrate 52a of the mother substrate 52 faces upward, as shown in FIG. 3E. The breaking bar 54 is then arranged on the TFT substrate 52a of the inverted mother substrate 52. A predetermined pressure is then applied to the breaking bar 54 to thereby cause the C/F substrate 52b to separate into the unit liquid crystal panels.
As shown in FIG. 3F, separated pieces of the mother substrate corresponding to respective unit liquid crystal panels are then unloaded. That is, the separated substrate pieces are simultaneously lifted from the table 51 by using a suction cup assembly (not shown). The substrate pieces are then fed to a station for subsequent processing.
FIG. 4 illustrates the arrangement of scribing and breaking devices included in the conventional substrate cutting apparatus.
FIG. 4 shows the related art substrate cutting apparatus that includes a loader 70 for receiving a mother substrate, where the mother substrate includes a TFT substrate 60 and a C/F substrate 65 joined together. The mother substrate is loaded while being seated on the loader 70. A first scriber 71 forms cracks in the mother substrate seated on the loader 70 along separation lines on the TFT substrate 60 of the mother substrate. A first breaker 72 applies a force to the cracks formed by the first scriber 71 at the side of the mother substrate opposite to the TFT substrate 60, thereby cutting the TFT substrate 60. The substrate cutting apparatus also includes a second scriber 73 for forming cracks in the mother substrate seated on the loader 70 along separation lines on the C/F substrate 65 of the mother substrate. A second breaker 74 applies a force to the cracks formed by the second scriber 73 at the side of the mother substrate opposite to the C/F substrate 65, thereby cutting the C/F substrate 65 to completely separate the mother substrate into substrate pieces corresponding to unit liquid crystal panels. The substrate cutting apparatus further includes a suction cup assembly 75 for simultaneously lifting and feeding the separated substrate pieces, a separation table 76 for separating the separated substrate pieces from the suction cup assembly 75, and an unloader 77 for transferring the separated substrate pieces from the separation table 76 to a station for subsequent processing.
The suction cup assembly 75 moves between the second breaker 74 and the separation table 76 to feed the substrate pieces, i.e., the unit liquid crystal panels, completely separated by the second breaker 74 to the separation table 76. The substrate cutting apparatus further includes conveying rollers 78 and a robot 79 to feed the mother substrate to a desired station during the scribing and breaking processes.
However, the above-described related art substrate cutting apparatus and method have numerous problems.
That is, the recent trend of LCD devices is to provide a larger display, so that it is necessary to use scribing and breaking devices adapted to an increased size for the processing of larger substrates. As a result, these large scale scribing and breaking devices must occupy a large part of a clean room. To this end, scribing and breaking processes for cutting of TFT and C/F substrates are respectively carried out at different locations. As a result, excessive space is required and the productivity degrades.